Update buildpack to support node 8.11.1 and yarn 1.6.0
Update buildpack to support node 8.11.1 and yarn 1.6.0

uktrade/data-hub-frontend,uktrade/data-hub-fe-beta2,uktrade/data-hub-frontend,uktrade/data-hub-fe-beta2,uktrade/data-hub-frontend